The invention relates to a method of detecting oscillatory variations in the magnitude of a quantity such as, in particular, oscillatory variations in the rate of rotation (rpm rate) of an input shaft of a cone-pulley transmission in the power train of a vehicle.
FIG. 2 presents a schematic view of a power train of a vehicle that is equipped with a cone-pulley transmission.
An internal combustion engine 2 is connected by way of a clutch 4 to the input shaft 6 of a cone-pulley transmission 8. The output shaft 10 of the transmission 8 is connected by way of a differential 12 to the driven wheels 14 of a motor vehicle. The cone-pulley transmission 8 has two pairs of conical discs and a flexible torque-transmitting device 16, e.g., a chain or belt, running in an endless loop around the pairs of conical discs. The transmission ratio can be changed by increasing the distance between the conical discs of one pair while simultaneously decreasing the distance between the conical discs of the other pair.
The power train is controlled by a control unit 18, which receives signals through inputs 20 from a drive pedal 22 and from sensors (not shown in the drawing) that register, e.g., the rpm rate of the internal combustion engine, the dynamic torque load on the combustion engine, the rpm rate of the transmission input shaft 6, the rpm rate of the transmission output shaft 10, etc. The outputs of the control unit 18 are connected to an actuator member 24 for setting the engine load, to the clutch 4, and to actuators for setting the ratio of the cone-pulley transmission 8.
The structure and function of the individual modules of the power train of FIG. 2 as well as the ways in which they interact with each other are known per se and will therefore not be further explained.
Torsional vibrations are frequently a problem in vehicle power trains, e.g., oscillations of the rpm rate of the input shaft 6 of the cone-pulley transmission 8, which can be caused by a variety of dynamic factors. These oscillations in the rpm rate, which can be detrimental to the comfort of the occupants of the vehicle, often occur in a range between 0.5 and 5 Hz. To detect such rpm-rate oscillations reliably poses a problem, because it is frequently impossible to ascertain whether a change in the rpm rate is caused by a change of the torque load, a controlled and/or regulated change of the transmission ratio, a change in the amount of slippage occurring in the clutch, and so forth. If oscillations in the rpm rate are identified as unintended oscillatory variations, it is possible to activate oscillation-damping algorithms that are stored in the control unit 18.
It is therefore the object of the present invention to provide a method by which rpm-rate oscillations of the kind described above can be reliably detected.
To meet the foregoing objective, the invention provides a method of detecting oscillations of a variable quantity. In particular, the method serves to detect the rpm rate of the input shaft of a cone-pulley transmission in the power train of a vehicle. According to the inventive method, a time derivative (i.e., a rate of change, herein also referred to as a time gradient) of the variable quantity that is prone to oscillations, or at least a value that is related to that time gradient, is registered over the course of a predetermined time period. The difference between the maximum and minimum levels that the registered value reaches during the predetermined time period is compared to a threshold reference. If the difference between the maximum and minimum exceeds the threshold reference, the variable quantity is judged to be in a state of oscillation. Surprisingly, this proves to be a reliable way of detecting the presence of an oscillation, which can then be counteracted through an appropriate use of control algorithms.
In a particular embodiment of the inventive method, the value that is being registered is the difference between the time gradient of the variable quantity and a reference gradient.
Any embodiment of the inventive method may also include a feature whereby the method is not carried out when certain predetermined conditions are present that have an influence on a change of the variable quantity.
In a particular embodiment of the invention, the variable quantity that is prone to oscillations is the rpm rate of the input shaft of a cone-pulley transmission of a vehicle, and the quantity that is being registered is the time gradient of the rpm rate of the input shaft.
In a variation of the preceding embodiment, the variable quantity that is prone to oscillations is again the rpm rate of the input shaft of a cone-pulley transmission of a vehicle, while the quantity that is being registered is the time gradient of the engine rpm rate, the transmission ratio, the output rpm rate of the cone-pulley transmission, or the vehicle speed.
As mentioned above, the inventive method may include a feature whereby the method is not carried out when certain predetermined conditions are present. In particular, such predetermined conditions include one or more of the following:
a) a control target set for the time gradient of the transmission input rpm rate exceeds a predetermined threshold level;
b) the time gradient of the engine-torque exceeds a predetermined threshold level;
c) the time gradient (rate of change) of the amount of drive-pedal depression exceeds a predetermined threshold level.
The inventive method is suitable for detecting oscillations in substantially all kinds of quantities that are capable of oscillatory variation, including mechanical oscillations, linear or rotatory oscillations, oscillations of electrical parameters, etc., to name only a few. The invention is particularly well suited for detecting oscillations of the rpm rate in the power train of a motor vehicle, especially the input rpm rate of a cone-pulley transmission that is part of the power train.
The novel features that are considered as characteristic of the invention are set forth in particular in the appended claims. The improved apparatus itself, however, both as to its construction and its mode of operation, together with additional features and advantages thereof, will be best understood upon perusal of the following detailed description of certain presently preferred specific embodiments with reference to the accompanying drawing.